The present invention relates to a tape reel to be applied to a magnetic tape cassette and, more particularly, to the tape reel having an upper flange and a lower flange provided at an upper end and a lower end of a hub, respectively.
Conventionally, there have been various types of magnetic tape cassettes for a video, for an audio apparatus, for a computer, etc. Some of the magnetic tape cassettes for videos, for example, are constructed such that a pair of tape reels is contained in a cassette case consisting of an upper cassette half and a lower cassette half. The pair of tape reels each has a hub, an upper flange and a lower flange. A tape reel rotates in a state where a magnetic tape has been wrapped around an outer periphery of the hub.
FIG. 4 shows one example of a tape reel. This tape reel 110 has a cylindrical hub 111, an upper flange 112 in a disc-like shape which is fixed to an upper end of the hub 111, and a lower flange 113 in a disc-like shape which is integrally molded with the hub 111 at a lower end of the hub. A magnetic tape 120 is adapted to be wrapped around an outer peripheral surface of the cylindrical hub 111.
A distance between the upper flange 112 and the lower flange 113 is set to be appropriately larger than a width of the magnetic tape 120. In this example, the magnetic tape 120 is wrapped around the hub 111 in such a manner that a clearance is created between an upper face of the lower flange 113 and an end of the magnetic tape 120 in a width direction of the magnetic tape 120. According to the cases, the magnetic tape 120 may be wrapped around the hub 111 in such a manner that the end of the magnetic tape 120 may be contacted with the upper face of the lower flange 113 in the width direction.
In recent years, for the purpose of improving volumetric recording density, the magnetic tape has been made thinner, and for the purpose of improving planimetric recording density, tracks have been made narrower.
As the magnetic tape has been made thinner, deformation of the magnetic tape in a width direction thereof has become likely to happen. For example, on occasion of high-speed running or acceleration or deceleration of the magnetic tape in a recording and reproducing apparatus, the magnetic tape may sometimes be deformed in the width direction. In addition, the magnetic tape may sometimes be locally brought into tight contact with guide rollers or the like. That results in the occurrence of curving or weaving of the magnetic tape. Moreover, due to the deformation of the magnetic tape, the ends of the magnetic tape in the width direction may come in contact with the lower face of the upper flange and the upper face of the lower flange, resulting in occurrence of the abrasion powder. This abrasion powder will incur an increase of dropouts. Particularly, when an amount of the magnetic tape wrapped around the hub is small, there will be a long distance from outer circumferential edges of the upper and the lower flanges to a face of the most outer layer of the magnetic tape already wrapped. Therefore, it is difficult to move the magnetic tape for this long distance without a hard or forceful contact with the lower face of the upper flange and the upper face of the lower flange in the width direction. If the magnetic tape comes in forceful contact with one of the lower face of the upper flange and the upper face of the lower flange on this occasion, the ends of the magnetic tape may be damaged, or abrasion powder may occur.
In the meantime, as the tracks of the magnetic tape have been made narrower, a so-called “linearity defect,” wherein reproduction output power at the deformed portion of the tape becomes lower than that at a rectilinear portion, has become likely to occur. Even with a minute deformation of the tape, the linearity defect may occur. The above described weaving of the magnetic tape will incur an increase of the linearity defects, that is, will incur an increase of fluctuations in the reproduction output.
Further, a so-called “irregular wrapping” is likely to happen, as the magnetic tape has been made thinner. For example, as shown in FIG. 5, which is an enlarged perspective view of a part A in FIG. 4, a portion of the lateral end of the magnetic tape may jump out from a plane composed of the other lateral ends of the magnetic tape in the width direction. As shown in FIG. 5, the portion 120a of the end of the magnetic tape that has jumped out is deformed so as to meander. When the magnetic tape has been deformed, normal recording and reproduction cannot be expected. Therefore, it is an extremely important problem to prevent such an irregular wrapping.
Although various factors are considered as causes of occurrence of the irregular wrapping, it may-be considered as one of the causes that when the magnetic tape 120 is wrapped around the hub 111 of the tape reel 110, air may intrude between adjacent magnetic tapes, and when the air escapes, it may push up the magnetic tape.